Age and its effect on sex hormones

Sex hormones follow a trajectory. They rise through adolescence, plateau in early adulthood, and then decline — gradually and steadily in men, more abruptly in women around menopause.

None of that is preventable, and it is not meant to be. But the shape of the curve varies between people, and some of that variation is associated with things you can influence.

The pattern in men

Three markers do most of the work: total testosterone, free testosterone, and sex hormone binding globulin (SHBG).

Testosterone production begins at puberty, climbs through adolescence and early adulthood, and levels off through the thirties. From around age 40 it declines at roughly one to two per cent a year, with the rate picking up after 70.^{1, 2}

Free testosterone — the portion not bound to protein and available to tissue — falls faster, at something closer to two to three per cent annually.³ That happens for two reasons at once: total testosterone is falling, and SHBG is rising by around one to two per cent a year. Since SHBG binds testosterone, more of it means less free hormone available even when the total looks steady.

This is why total testosterone alone can be misleading in older men. The total can sit comfortably in range while the free fraction has moved considerably.

The pattern in women

The useful markers differ. Testosterone still matters, at much lower concentrations, but DHEAS and SHBG carry more of the picture.

DHEAS is often preferred because it stays relatively stable across the menstrual cycle, which makes it easier to interpret from a single sample. Levels are highest at birth, drop through childhood, climb again at puberty and peak in the mid-twenties, declining steadily from there.⁵

Testosterone in premenopausal women peaks around day 14 of the cycle — which is why timing matters so much for testing. Across the menopause transition it falls by roughly 15 per cent and then broadly stabilises.^{6, 7}

SHBG in women tends to stay reasonably stable across life, but it is sensitive to outside influences. Hormonal contraception can shift it substantially depending on the method, and metabolic factors including obesity, larger waist circumference and type 2 diabetes are associated with lower levels.⁸

What the decline is associated with

Research has identified several factors that track with faster or slower hormonal change. These are associations rather than instructions, and none of them stop the underlying process.

Body composition shows the strongest and most consistent relationship. Obesity is associated with faster testosterone decline in men, and with lower SHBG in women.¹

Physical activity — both aerobic and resistance training — is associated with better preservation of lean mass and more stable hormone levels across both sexes.

Metabolic health matters. Type 2 diabetes and high blood pressure are both associated with lower testosterone in men, and with disrupted hormone balance in women.¹

Smoking is associated with faster decline.

Psychological factors appear in the research too. Depression, sustained stress, and major life disruptions such as job loss or bereavement have all been associated with faster testosterone decline in men.^{1, 3}

Short-term fluctuation sits on top of all of this. Sleep, training load, illness and stress move hormone levels week to week, independently of the longer trajectory — which is a large part of why a single reading is hard to interpret and why timing and consistency matter when retesting.

What this doesn't tell you

• It isn't a diagnosis. Hormone results need reading alongside symptoms, history and examination by a doctor.
• Associations aren't causes. Factors that track with slower decline in population research may not do the same in any individual.
• Age-related change isn't automatically a problem. A declining curve is the normal biological pattern, not a condition by default.
• Never change prescribed medication on the basis of an article or a test result. That is a conversation with your doctor.

The bottom line

Sex hormones change with age on a fairly predictable curve, and the useful markers differ between men and women — total and free testosterone with SHBG for men, testosterone with DHEAS and SHBG for women.

A baseline measurement is what makes any of it interpretable later. Without one, a result in your fifties is a number without a reference point.